Conjugative effects in W(CO)₅ complexed phosphirane rings illustrated by substituent effects on ³¹P NMR chemical shifts

Correlations between ³¹P NMR chemical shifts and Hammett σ substituent constants are reported for a total of 22 anti- and syn-phosphiranes, obtained from the reactions of the carbene-like phosphinidenes PhPW(CO)₅ and H₃CPW(CO)₅ with various para-substituted styrenes. The origins of these four sets of correlations with respect to electronic and electrostatic interactions are discussed. Arguments are presented that strongly suggest significant conjugation between the remote p-X-phenyl and trans-P-phenyl groups in the syn-1 substituted phosphiranes. Electrostatic forces do not play an important role in these PW(CO)₅ complexed phosphiranes and neither do steric interactions.